Spatial light modulator projection display systems create a full color image from a beam of white light in one of two different ways. A first type of display separates the white light into the three primary colors and simultaneously modulates the three primary color light beams. The three modulated light beams are then recombined to form the full color image. This type of display requires three modulators and typically uses a set of dichroic crosses or a color splitting prism assembly.
The second type of display is a sequential color display. Sequential color displays sequentially filter the beam of white light to create a single filtered beam whose color alternates over time between the three primary colors. A single modulator modulates the filtered beam of light in synchronously with the filter sequence to produce three primary colored images in rapid succession. The viewer's eye integrates the three sequential images to provide the perception of a full color image.
Sequential color displays require a faster modulator in order to be able to generate three separate images within the frame period. Sequential color display systems typically use simpler optics and require less alignment and are therefore typically cheaper to produce. Unfortunately, because only one third of the available light is being used at any given time, sequential color systems produce dimmer images compared to three color systems using the same light source.
One method of increasing the brightness of sequential color display systems is to include an additional period during which white light is modulated. The white period increases the available light, but reduces the color saturation of the image. The tradeoff between brightness and saturation results in a compromise that is based on how the projection system will be used. What is needed is a method and system to improve the compromise between increased brightness and color saturation.